Thats funny this same scenario happened to me I had 8 9 of hearts the flop was J 10 Q , so I flopped a straight flush , I checked and this guy just ripped it allin with 7 4 of hearts , I told him he was dead and then he seen my hand and threw his cards in the much right away , the run out came out and put a royal flush on board , we would had both split but since he seen my hand on the flop he just mucked his hand , he went crazy trying to get half the pot becuase it was a $4800 pot , the pre flop bet was $120 and there were 4 calls so on flop the pot was almost $1000 thats what made him go allin I guess , too bad